The present invention relates generally to supporting the face of a passage in a geological structure, and more particularly, to a truss system for supporting a mine roof and a related installation method.
In recent decades, a number of proposals for supporting the face of a passage in a geological structure, such as the roof in an underground mine, have been made. The typical arrangement employs anchors, such as roof bolts, that extend into spaced bores drilled in the face at opposed angles. A support bracket secured to each angled anchor external to the corresponding bore provides support for a horizontally extending truss member. Depending on the particular application, the truss member may be a cable or metal rod, the ends of which are initially secured to the corresponding bracket by hand. Once secured in place such that it spans between the brackets, the truss member is tensioned to compress and provide support for the adjacent face. Typically, tensioning is either completed manually or by using hand-held power tools.
As explained in my prior U.S. Pat. No. 5,755,535, the major shortcomings of prior art systems include: (1) the relatively large number of diverse parts required to form the truss system, which increases the manufacturing cost; and (2) the difficulty in providing the proper tensioning for the truss member to create the desired level of support. Also, most systems require the installer to determine the length of the truss member with some precision prior to installation to ensure full tensioning. Of course, this increases the overall time required for installation, which is often regarded as a critical factor in determining whether a particular truss system is commercially viable.
To overcome these shortcomings, the ""535 patent discloses an improved truss system and related installation method that represents in some respects a radical departure from the approach taken in the prior art. This system reduces the number and diversity of parts required by using identical brackets that not only connect with both the anchor and the truss member, but also serve to support the face adjacent to each borehole when the truss member is properly tensioned. During installation, a drive adaptor allows a rotational socket on a drill head of a bolting machine to provide the necessary torque required for tensioning the horizontal truss member (either a cable or metal rod). This fully eliminates the problems associated with manual tensioning or the use of hand-held power tools. Since a lifting mechanism is available to raise the rotational socket/drill head into the desired position, this also reduces the amount of effort required by the installer, as well as the concomitant incidence of fatigue, especially for installations on mine roofs. Finally, instead of a rotary fastener, a split-wedge retainer holds one end of the truss member securely in a frusto-conical passageway formed in the bracket. Since the corresponding end of the truss member need not be threaded, this eliminates the need for precisely determining the length of the truss member required prior to installation to ensure that full tensioning is reliably accomplished. Overall, the result is a simplified, but exceedingly reliable truss system and installation method.
Despite this significant advance set forth in this earlier ""535 patent, I have discovered that there exists an opportunity to provide a highly reliable truss system that is even less costly to manufacture, as well as even simpler and less time consuming to install. Of course, one of the major areas for lowering the manufacturing cost and installation time is to reduce even further the overall number, diversity and complexity of the parts required. This includes eliminating the need for specialized adaptors to transmit driving torque from the bolting machine during tensioning. Moreover, the system would still remove not only the need for threading one or both ends of the truss member, but also the need for precisely determining the length of the truss member required prior to installation to ensure proper tensioning. Overall, the resulting truss system would provide full strength support for the face at a lower manufacturing cost and with less installation effort required.
Keeping the above needs in focus, it is a primary object of the present invention to provide a truss system for supporting the face of a passage in a geological structure that further overcomes the shortcomings and limitations of the prior art systems.
Another object of the present invention is to provide a truss system including spaced borehole anchors carrying truss support brackets positioned in the borehole and at least one truss member that spans between the brackets, wherein the truss member is set up and tensioned by moving either or both of the brackets along its corresponding anchor.
Still another related object of the present invention is to provide a tension-activated truss system wherein the force for moving the truss support brackets along the corresponding anchor and into the borehole is provided by a bolting machine, whereby the need for manual force or hand-held power tools to provide the necessary tensioning action is eliminated.
A further object of the present invention is to provide a truss support bracket that is drawn along an anchor adjacent its borehole and into the corresponding borehole during tensioning, while a separate face support or plate carried by the truss member engages and supports the adjacent face of the passage.
Yet another object of the present invention is to provide a preferred truss system wherein at least one of the truss support brackets is capable of taking up any slack in the truss member prior to tensioning, even when in position in the borehole, thereby eliminating the need for precisely determining the length of the truss member required prior to installation.
A related, but more specific, object of the present invention is to provide a truss support bracket that carries a split wedge retainer for receiving and capturing an end portion of the truss member, whereby the need for threading the corresponding end of the truss member for receiving a rotary fastener or the like is eliminated.
Still a further object of the present invention is to provide a related method of installing a truss system wherein only a selected one of the truss support brackets needs to move along the corresponding anchor into the borehole after initial set up of the system in order to tension the truss member.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an improved truss system and related installation method are provided for supporting a face of a passage in a geological structure, such as a mine roof. In its broadest aspects, the truss system of the present invention includes first and second anchors that are positioned in spaced boreholes formed in the selected face of the passageway. A truss support bracket is positioned adjacent its borehole on each anchor and held in position by a fastener. At least one truss member, such as an elongate cable, spans between the brackets, and a motive device is provided for engaging a selected one of the fasteners to move the associated bracket further along the anchor and deeper into the corresponding borehole. As should be appreciated, as the bracket moves deeper into the borehole, the truss member is tensioned to compress and provide support for the adjacent face of the passage.
In the preferred embodiment, the selected fastener for holding the bracket in place and moving it into the corresponding borehole is a rotary fastener threaded to the proximal end of the corresponding anchor. The motive device for engaging this fastener is a rotational socket of the type provided on the drill head of a standard bolting machine, which is of course typically employed to drill boreholes and install face anchors, such as roof bolts. The preferred form of rotary fastener is an elongated nut, but of course other equivalent types of connectors or fasteners may be employed for holding the corresponding bracket in place and moving it along the anchor during tensioning.
As should be appreciated, once the anchors are positioned in the boreholes, the selected fastener holding the bracket in place is positioned adjacent the face, but just inside the borehole. To transmit torque from the rotational socket to this selected fastener when positioned in the borehole opening, an extension tool, such as an elongate wrench having a deep well socket head, is used. This elongated tool ensures that the desired engagement with the fastener is maintained at all times as it is drawn along the corresponding anchor further into the borehole, and eliminates the need for the multiple repositioning of the rotational socket during installation.
By using the rotational socket on a bolting machine to provide the desired tensioning, the need for employing manual tools or heavy, awkward hand-held power tools is eliminated. Moreover, the amount of tension supplied may be precisely controlled, since the rotational socket on the standard bolting machine is limited by a built-in torque control feature. The use of a bolting machine is also particularly advantageous when the truss installation is coupled to a mine roof since: (1) the lifting mechanism may be used to raise the rotational socket into position for installing the anchors, as is known in the art, as well as to move the wrench or other extension tool into the hole such that the fastener remains fully engaged during tensioning; and (2) pivotal mounting of the drill head allows the drill head to tilt in a horizontal plane such that the socket/extension tool may be aligned with the fastener in the angled borehole. Of course, this potentially infinite adjustability of the rotational socket/drill head makes the overall tensioning operation simplified and easier for the installer(s).
In one particularly preferred embodiment, each bracket is identical and includes a first passageway for receiving the proximal end of the corresponding anchor and a second passageway for receiving an end of the truss member. The second passageway is tapered or frusto-conical and carries a retainer, such as a split wedge retainer, that captures the corresponding end of the truss member during installation. As should be appreciated, the use of a split-wedge retainer is advantageous for several reasons. First, it eliminates the need for threading the end of the truss member and providing the associated rotary fastener required in many prior art systems that is easily lost or misplaced during installation. Secondly, it allows the installer to feed the end of the truss member blindly through the bracket into the borehole as necessary to reduce the amount of slack prior to tensioning. Advantageously, the wedge halves automatically separate in unison upon engagement to allow the end of the truss member to pass. To prevent the bracket from moving along the anchor during this operation, a first stop is carried on each anchor adjacent to the bracket. However, this stop does not prevent the bracket from moving into the borehole when the selected fastener is engaged. Also, the second passageway in each bracket includes a second stop to capture the retainer therein and prevent it from backing or lifting out of the bracket as the end of the truss member is inserted.
During the preferred installation, a first bracket is placed adjacent its borehole and drawn up on its anchor. A first end of the selected truss member is installed in the corresponding bracket by passing it through the corresponding split wedge retainer. The portion of the truss member extending out of the borehole is then manually tugged such that the split wedge retainer is snugged into place in the frusto-conical passageway. In this position, the retainer is seated in this passageway such that it grips the truss member and securely holds it in place. Then, the opposite bracket is placed adjacent its borehole and drawn up, whereupon the corresponding end of the truss member is blindly inserted into the corresponding passageway of the bracket. This opposite end is fed through the passageway until substantially all of the sag is eliminated, and then the portion of the trust member extending out of the borehole is manually tugged to seat the corresponding split wedge retainer in the passageway. Preferably, the truss member is then tensioned by engaging only a selected one of the fasteners to move the corresponding bracket further into the borehole. If necessary, both fasteners may be engaged for tensioning the truss system, depending on mining conditions, practices and equipment.
As should be appreciated, since each end of the truss member may be passed completely through the corresponding retainer in each bracket and into the borehole, the present system allows for the installer to roughly approximate the length of the truss member required for a particular installation. This of course advantageously eliminates the need for precisely calculating the length of the truss member required prior to installation. Any slack is taken up by simply forcing the one or both ends of the truss member further into the borehole until it spans between the brackets adjacent to the face. This flexibility eases the installation process, which serves to reduce the overall cost. Also, it facilitates installation where the approximate spacing of the boreholes is known, but the face of the adjacent passageway is graded or uneven.
At least one, and most preferably a pair of supports in the form of plates are carried on the truss member. These support plates serve to engage the face adjacent to the boreholes when the truss member is fully tensioned. Each plate preferably includes an eyelet through which the corresponding end of the truss member is inserted just before it is passed into the associated bracket. Preferably, during the installation of the truss system of the present invention, stops are placed on the truss member to ensure that the supports are held adjacent to the borehole at all times. This allows the operator to focus on the installation of the truss member and not worry about the positioning of the support plates until the system is ready for final tensioning.
To install the truss system of the present invention, and in accordance with the related method described herein, the anchors are positioned in first and second spaced boreholes drilled in the face of the passage. In a most preferred embodiment of the installation method, the boreholes are drilled such that each includes xe2x80x9csteppedxe2x80x9d bores having different diameters. The first bore is oversized for receiving the bracket, while the second bore is sized for receiving the resin cartridge or expansion unit that serves to hold the anchor in position. As should be appreciated by those skilled in the art, the specific diameters and lengths of these stepped bores depend on the particular application or mine conditions encountered.
To secure the anchor in the borehole, any conventional means may be employed. As known in the art, a cartridge containing resin or grouting may be inserted in the borehole prior to insertion of the anchor, or an expansion unit may be deployed to secure the anchor to the rock or other material in which the borehole is formed. Additionally, a combination of the two technologies may be employed, as shown in my prior ""535 patent, the disclosure of which is incorporated herein by reference.
One of the truss support brackets is then positioned on each anchor adjacent its corresponding borehole as described above, and a truss member, such as an elongated cable, is attached to each corresponding bracket, preferably also in the manner described above, such that it spans across the adjacent face. Then, by moving a selected one of the brackets along the anchor further into the corresponding borehole, such as by engaging the corresponding rotary fastener with the rotational socket of a bolting machine, the truss member is automatically and fully tensioned.
Still other objects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.